Osteoclast More than twenty years ago Walker proved that bone resorbing cells called "Osteoclasts" came from hematopoetic precursors, Today other investigators have shown that osteoclasts were influences by systemic hormones (parathyroid hormone, 1, 25-dihydroxyvitamin D3, calcitonin), cytokines (IL-1, IL-3, IL-6,) and hematopoetic factors/colony growth factors. Yet most of these stromal or marrow cultures involved in vitro systems. My project uses an in vivo system that has been proven by Minkin (1991) to develop osteoclasts from their precursors in a chemically defined medium. I will characterize a gene related to osteoclastogenesis via a method called mRNA differential display developed by Pardee and Liang at Harvard Medical School. Metatarsals from embryonic mice were harvested at stages before and after osteoclast presentation, RNA extracted, and cDNA probes made via PCR. Currently, hands are being sequenced.